1. Technical Field
The present invention relates to a semiconductor device and a booster circuit. In particular, the invention relates to a device that is applied to a method for improving the mobility of transistors used in a charge-pump circuit.
2. Related Art
Along with the progress of semiconductor manufacturing process in recent years, the denser integration and more function multiplication of semiconductor integrated circuits have been being accelerated, and the power supply voltage inside a semiconductor integrated circuit has been becoming lower. In addition, accompanied by the more function multiplication of semiconductor integrated circuits, the embedding of various power supplies, including high-voltage power supplies, has also been increasing. For example, non-volatile memories such as flash memories, EEPROMs, etc. and driver ICs of indicating elements such as liquid crystal, etc. require a high voltage of 10 V or more. Therefore, as a booster circuit for generating such a high voltage, a charge-pump method that enables an easy embedding into semiconductor integrated circuits has been employed in place of a switching regulator method using coils, etc. As such a charge-pump method, Dickson charge-pump circuits are generally used, as disclosed in an example of related art: JP-A-2004-328901.
In the above charge-pump circuit, however, the substrate terminals of transistors need to be grounded for the purpose of latchup prevention. Therefore, transistors configuring a charge-pump circuit need to have a high breakdown voltage. Since such a configuration raises the internal impedance of a charge-pump circuit, there has been a problem of the degradation of conversion efficiency.